The invention relates to the field of display devices for reproducing optical information. In particular, the invention relates to display devices which are based on the use of liquids for visualization of information.
From the prior art there is known an almost overwhelming variety of display devices serving the reproduction of optical information, such as e.g. text, still images or even moving images (videos). While a large proportion of these display devices in particular serves to reproduce colored and quickly varying information, solutions also exist which focus on the reproduction of more static and optionally monochrome information.
As an example for such display devices, reference is made to the technology of “electronic paper” developed by the company E Ink (Cambridge, Mass./USA; www.eink.com). The document U.S. Pat. No. 6,120,588 (“Electronically addressable microencapsulated ink and display thereof”) is mentioned in this respect. Herein, a plurality of tiny globules is used which can be oriented in an electrical field and which are, for example, colored in white and black in equal share. By specific application of certain display areas with a corresponding electrical field, these areas appear to be colored, whereas other areas appear uncolored. To enhance contrast, an opposed electrical field can be applied to the remaining areas. In particular advantageous is the fact that such devices can be operated with low power, however, they offer slow reaction times and moreover the disadvantage that only a few colors can be displayed.
A different principle is for example disclosed in document U.S. Pat. No. 7,304,786 owned by the company Liquavista (NL). The method described herein is based on use of colored liquids, more specifically of a two phase mixture made up of colored liquid (oil) and a carrier liquid (water). Switching of a single image dot (“pixel”) is carried out by means of the effect of electrowetting. By means of this effect, the shape of the oil droplet inducing the color impression can be changed. However, the amount of colored liquid present in a respective image dot is constant and can only be modified with respect to its shape. By utilizing the effect of electrowetting, energy input can be dramatically lowered, since power needed therefore is comparatively low. In a rest position, the colored liquid is uniformly spread over the area of an image dot, without supplying power, resulting to a correspondingly fully covered, colored image dot. Due to the used liquids, however, such display devices are suitable only for operation at normal ambient temperatures. Furthermore, the pixels merely include one single color, so that display of plural different colors can only be achieved by means of a close arrangement of differently colored “subpixels” and use of optical fusion thereof to perceive one pixel. Aging finally leads to undesired degradation after a while which cannot be remedied, since due to the fixed volume of colored liquid of an image dot no exchange of degraded liquid is possible.
Such fluidic devices which are based on the use of colored liquids often include single display elements (“pixel”) consisting of two chambers, one of them serving for display, whereas the other one is used as a reservoir, if the corresponding pixel is not being displayed. These constructions are both complex and error-prone. A further disadvantage is seen in the fact that such two chamber solutions comprise a respective higher footprint, unless the chambers are respectively underlying the corresponding image dots, which in turn leads to fluidically complex constructions.
U.S. Pat. No. 3,566,172 A discloses a display device wherein information to be displayed is represented by means of a liquid and wherein a plurality of display elements is fluidically connected to a common liquid reservoir. A display liquid is delivered to or from the driven display element by means of at least one pump as well as valves.
WO 03/071335 A2 discloses a display device wherein with the aid of the effect of electrowetting the surface geometry of a liquid droplet can be manipulated such that the focus of a liquid droplet acting as a lens can be adjusted as a result of the modification of geometry.